Hydraulic fracturing is a primary tool for improving well productivity by placing or extending cracks or channels from the wellbore to the reservoir. This operation is essentially performed by hydraulically injecting a fracturing fluid into a wellbore penetrating a subterranean formation and forcing the fracturing fluid against the formation strata by pressure. The formation strata or rock is forced to crack, creating or enlarging one or more fractures. Proppant is placed in the fracture to prevent the fracture from closing and thus provide improved flow of the recoverable fluid, i.e., oil, gas or water.
The proppant is thus used to hold the walls of the fracture apart to create a conductive path to the wellbore after pumping has stopped. Placing the appropriate proppant at the appropriate concentration to form a suitable proppant pack is thus critical to the success of a hydraulic fracture treatment.
The geometry of the hydraulic fracture placed directly affects the efficiency of the process and the success of the operation. This geometry is generally inferred using models and data interpretation, but, to date, no direct measurements are available. The present invention is aimed at obtaining more direct measurements of the fracture geometry (e.g. length, height away from the wellbore).
The fracture geometry is often inferred through use of models and interpretation of pressure measurements. Occasionally, temperature logs and/or radioactive tracer logs are used to infer fracture height near the wellbore. Microseismic events generated in the vicinity of the created hydraulic fracture are recorded and interpreted to indicate the direction (azimuth) and length and height of the created fracture.
However, these known methods are indirect measurement, and rely on interpretations that may be erroneous, and are difficult to use for real-time evaluation and optimization of the hydraulic fracture treatment.
It is therefore an object of the present invention to provide a new approach to evaluate the fracture geometry.